Gear finishing



March 27, 1945. M. B. M ENTLEY 2,372,444

GEAR FINISHING Filed March 30, 1942 INVENTOR.

MAX B. MENTLEY ATTORNEYS Patented Mar. 27, 1945 GEAR-FINISHING MaxBhMentley, Detroit, Mich., assignor to National Broachand Mach neCompany, Detroit, Mich, I a corporation of Michigan Application March30, 1942, Serial N0."436,897

6 Claims.

The present invention relates to gear finishing and more particularlytoa method ofsimultaneously crowning and shaving gears.

The method employed is an improvement over. crossed axes gear shaving inwhichthe gear and agearlike shaving tool are-meshed with their axescrossed at a limited angle; The gear" and tool are rotated in mesh, andthe relative' translation between the gear and tool is effected wh chdistributes finishing action of the tool longitudi= nally of the gearteeth.

Ithas heretofore been suggested that' gear teethcould be crowned duringthis operation; by effecting an additional relativefeed between, the

gear and tool in adirection radial of i the .gear,

in which the additional feed'was carried out in timed relation tothetranslation. In some. cases good results could be" obtained by thismethod v but it has-been found thatbettergresults are ob tained when themethodi modified as disclosed herein. I

It is an objectLof'the presentinvention to provide a method of shavinggear teeth which comprises employing cuttingedges on the cutter teethwhich are substantially adjacent the ends thereof.

It is a further object of. thepresentlinvention to provide a method forshaving. gear v teeth. by

Y rolling the gear'in mesh atlcrossed :axes with the shaving tool, andeffecting: the relative crown toolibeing moved into clearancepositionduring? the back strokel 1 It is a furthervobject of ztherinvention'to'shave gears by themethod as referred to above,,in' whichvthedirection of rotation of'the gear and adjustment of tool between rightand left cutting strokes; and

Figure 5 is a diagrammatic view similar to Figure 3; showingtherelationship between' gear and tool upon" commencing to cut the righthalf of thegear teeth. I

Referring first to Figure 1; I have shown'at lfl' a gear" tooth which iscrowned. The crowned shape ofthe tooth, as seen in Figure 1, appears ascurved'line l I and I2 showing the longitudinal curvature of'the toothIll. The" crowned shape of the tooth may be considered as longitudinalrelief so that the tooth is'thicker at its mid section than at eitherend thereof.

Teeth ofthis' shape are com ng into increasing demandfor the reason thatthey operate more quietly thanuncrowned teeth and permit certain amountsof shaft mi'salignmentor distortion under'load without cr'eating'strict'end bearing between meshing'gear teeth. This avoidance of end bearingresults in greater 'tooth'lifesince it has been found that a largeproportion of gear failures is directly attributable to end bearing.

Various methods have'previously been suggested for crowning gear teeth,and-amongth'ese is a method disclosed in Drummond Patent2;1"5'7,981',-in which a relative rocking motion is effected between the gear and toolduring a crossed axes shaving operation.

toolarereversed when cutting operation reaches the middleof thegeartooth;

Other.v objects of the inventionwill bev-appars I ent as .the..description proceeds; and: when taken drawing;

in conjunction with .the accompanying wherein:

Figure 1 is a perspective-view of a crowned gear tooth;

Figure 2 is a diagrammatcu view illustrating: the meshing 7 relationship.-l: etweenithe gear and tool;

Figure 3-is a diagrammatic view-illustrating the According to thepresent method the tool and gear to be crowned are brought into-meshwith their axes crcssed at an angle preferably less than 30". Thisresults in establishing a limited area of contact between the teeth ofthe gear meshing with the teeth of the tool, due to the crossed axesrelationship. When the gear and tool are then rotated in mesh thislimited area "of contact becomes a Iimited'Zone ofcontact extendinggenerally up and down the face of the teeth of the gear. During rotationof the gear and tool, one of'the parts is positively rotated andtheother part is driven solely through the meshed engagement between thegear and tool.

In order to distribute the finishing action of the tool'longitudinallyfrom end to end of the teeth of the gear, a relative'translation isintroduced. In Figure 2 1 haveillustrated diagrammatically'a tool'Tin'mesh with a gear G; The direction of rotation'is indicated by thearrows20. The relative translation which is necessary to distribute thefinishin'g'action of the teeth of the tool T longitudinally from end toend of the teeth of .the gear'Gis illustratedb'y the arrow 2|. If thistranslation is combined with the rotation without other relativemovementthe teeth of the gear G will be finished uniformly from end toend, or in other words they will be uncro-wned' In order to V impart acrowned shape to the teeth of the gear G,

a second relative motion in the direction of the arrow 22 is set upbetween the gear and tool in timed relation to the relativereciprocation represented by the arrow 2|. The timed relationshipbetween the radial feed indicated by the, arrow 22 and thetranslatiomindicated by the; arrow 2 I will" be explained. When the gearand tool are in that portion of relative translation which causes the.teeth of the tool to contact the teeth of the gear at their midportions, the axes of the tooliTrandz' the gear G are separated by amaximum distance. As translation takes place in .eit-heizdirecti'on fromthis mid position, it is combined with a" relative, feed radially inwardof the gear G. As willbe apparent, this has theefiectzofimachiningcreasingly more materia1 adjacent the ends of theteeth of the gear and therefore resultsinthe crownedtsha-peshownin-Eigure: 1.

One of the disadvantages of thia methodtisathatl it-has been found that:thaamountxofrcrownwhich can thusbe:imparted;.to=-the:teetlr:of.thergearris:

strietlyr'limited.,, Whileit.isitruethattheainstant I reshaving thecenter of:the;gearyteethlwitlrlaiporrtion :Ofi thescutter: removedrfromr thmzone: oi; the common; normal: to; the axes; off gear: andtook. This in, turn.=would introducesarproflleaerror; orr

require: modification: of; the-x cutterc-v Thisilastl vitsimpractical,-, becausesthe. cutter: is; still? operating; on anothenportion oie'the gearl teeth-1 adjacent; saidcommon: normal; and such:modification or; cutter teeth could :not therefore: beeuniform;

Accordingly; the presentl invention oonteme platesmeshing; the gear and111-0 01,, duringzgtheecutas seen in Figure 3, will be machined whilethe tool T moves to the dotted line position T. Then the gear and toolare moved in loose mesh and the tool is relatively moved back to fullline position. At this time one-half of each of the teeth of the gear ismachined.

In order to machine the other half of the teeth of the gear, it isdesirable to employ the opposi-t'e ends ofztlie teeth ofthe cutterandsfor this purpose the cutter is shiftedas shown in Figure In thisfigure, with the tool T in the fullline position relative to the gear G,it is neces sary, to shift it to the dotted-line position T if the otherend of the cutter teeth are to be used. 'li'liis may he done readily byshifting the tool axially'foradistance equal to its face width.

The" crown cutting of the other half of each of the. teethimay, then becarried out, as illustrated in Figure 5. In this figure it will beobserved that the, common normal X to the axis Ta roof? the tooLandlGmofthe :gear iseadjacent-lthe rights-hand, edge: of, thetool T- and.islocated midway between the. ends; of= the: teeth of) the gear so as toremove materiallfromhadjacentsthelelfi;...end,of-- theteethof .the:gearGs This results in,.shap ing,,the; teetlialofrl the gear to the-shapeillustratedlin Figural Before. the relative, translation betweenthc.

- gean'G;andjtool'lliszreverssdhthesparts .aramoved;

into? loose mesh, as previouslyd'escribedrin con, nection'withsFigure-Bl 1 40' dotted line" position T "to; iulllline position.

tinggoperationsuch that thercutting actiondsieis i'ectedzbyvportionsoi-therteeth offtheztooliadj acentv onesend. thereof-l.Whenathergea-rrand tooliareo meshedsatwcrossed, :axes;. the :contactrbetweerrrthw teeth thereof takes place in a zonerrattandfiad jacenttozther common .normal :to their: axesa ThusinwEiguresr-2-5sLhave:illustrated :the:toohT meshes ing; with la, gear-G: The :axisJIYa ofithestoolsisliL-w lustrated, ass is the axis: Ga ofthagear: The? common normal to theseaxes; which israalinerperpendicular-to the planaof thepaper:iseindicatech 7 ate XeIt:willtthuseberseenrthatr cutting-3 withxtha parts engaged as shownain; Figure: 3- takes i place;- adjacent the-.leftehandend of: theeteethof. the tOO1;-T..

If thaw-ta :rel-ativemotion between the-gear anclr tool :isI providedwhich lcauses-rtheetoolzT; to move inlthesdirectiontofztheearrowriill::(Flig. 3); wittr resspect to the gear G1; it will-:be-apparentdthatzassubs stantial. amount." of: crowning; motion: whiel'iis radially, inward,with respeetlto =the Grmayy be; provided. without-interferences;..

It. hastbeentfound-t that. theemost effectivee-cuteting,takesoplacerduring the;relative motiomwhichl causes the-tool,T-tomove;relativeetotheageanG-xinl the;directionoithaarrom 30:Aecordinglmwhem To:

The..right-.-hand half-of:theeteethyoflthergearrGir.

The method" as thus far described may; be;

- carried outwith the conventional r serrated shaving tool; whichzmaycut with cutting ,edges spaced.

somewhat from; the end ofithe teeth. If prelierred, however;undercertain circumstancesit.

may h e-possible" to employa cutter for cutting onlyonthe'corners"'of.the teeth In somecases it is desirable to" control thedirection oflrotation so' as 'ttrefiect'a cut; ,with the corners of theteeth; whether or not theteeth are serrated; At. any 'eventi hr order'toobtain'uniformresults at opposite ends ofthe-gcarteeth, itisrdesirablejto, reverse the rotation before commencing the cut at oppositeends of the gearte'eth.

' Referring" to Figure 1 3i the direction of. rotation" ofthe1gear-G andtool T is indicatedfiby'the.

arrows 3| and 32. Itwill be observed. that in this icase thedirectiomof*rotation'" of the tool T issucli th'atthe ends of "its teethadj acem; the

commonznormal Kare-"moved toward the center otzithegear so as' to:effect a cutting orshaving:

action. In this case, sinceno'portion of'tliecuti terr teeth: extends'beyond the cutting: edges toward the" center "of the gear teeth; there"can be spaced inwardly from the the ends of the' utter" teetlnwillsbeemployedl'to provide cutting'iedges;

either direction, but should be in opposite directions "at: opposite?ends of 'tl-i'e gear teeth to'pim suresuniform'@resultsa It will 'be:.appreciated that the relative" mo" tiorr whiclrlis due=:to ithe= crossedaxes= setting is Thisavoids. cuttinglwhilet return relative translation.is taking, place: from.

In: 1311185031585 thetsdirectiomofl'rotation Ama y be' in" relativelyrapid and is at cutting speeds due to the speed of rotation of the gearand tool. The relative translation in the direction of the arrow 30 isvery slow, as is the relative radial infeed.

When the cutting operation illustrated in Figure is being carried out,the direction of rotation of the gear and tool is of course reversed.Accordingly the relative motions between the gear and tool, which arenecessary to combining the shaving and crowning operation, are asfollows: At the beginning of the cutting stroke the gear and tool aremeshed such that the common normal to their axes is locatedsubstantially at the center of the gear and is located substantially atone edge of the tool or cutter. The direction of rotation of the gearand tool may be such that the ends of the tool teeth which are engaged,move forwardly across the face of the gear teeth toward the centerthereof, or op-- posite thereto. Relative translation moving the meshedteeth of the tool away from the center of the gear teeth and toward anend thereof is provided and is accompanied by a relative infeed radiallyof the gear. At the end of the stroke when the teeth of thegear havebeen machined completely to one end thereof, the gear and tool are movedinto loose mesh and are returned to initial position. Prior to the nextsucceeding the position shown in Figure 4, such that the opposite end ofits teeth are adjacent the common normal X. The direction of rotation isreversed and the translation in the direction of the arrow 40 iseffected to machine the other half of the teeth of the gear G. Thisoperation may be repeated with additional incremental feed as many timesas necessary to remove material to the proper depth, and the result isgear teeth which are not only smoothly shaved and corrected as toprofile, spacing, eccentricity, etc., but also the teeth have adesirable form of crowning imparted thereto.

It is appreciated that this method may be carried out on suitableautomatic machines, but it may also be carried out by a hand operationof standard machines available. today.

While the method has been described in considerable detail, it will beappreciated that this has been done solely to enable those skilled inthe art to practice the invention, the scope of which is indicated bythe appended claims.

What I claim as my invention is:

1. The method of crowning the teeth of a gear which comprises running itin mesh with a gearlike cutter such that only the end portions of theteeth of the cutter are employed, and taking cutting strokes beginningat the mid portion of the gear teeth and finishing at an end thereof byrelatively moving said gear and cutter such that the said cutter teethmove longitudinally relative to said gear teeth away from the operatingend portions thereof, returning said gear and cutter to approximatelyinitial position in loose'mesh, relatively shifting said gear and cutterto bring the other end portion of said cutter teeth into operativeposition to the centers of the gear teeth, and machining the oppositeends of said gear teeth in like manner.

2. The method of crowning the teeth of a gear which comprises running itin mesh with a gearlike cutter such that the end portions of the teethof the-cutter are employed, and taking cutting strokes beginning at themid portion of the gear teeth and finishing at an end thereof byrelatively moving said gear and cutter such that the said cutter teethmove longitudinally relative to said gear teeth away from the operatingend portions thereof, returning said gear and cutter to approximatelyinitial position in loose mesh, relatively shifting said gear and cutterto bring the other end portion of said cutter teeth into operativeposition to the centers of the gear teeth, reversing the rotation ofsaid gear and tool, and machining the opposite ends of said gear teethin like manner.

3. The method of crowning a gear which comprises meshing the gear With agearlike finishing tool with the axes of said gear and tool extending atlimited crossed axes, rotating said gear and tool in mesh, andrelatively moving said tool and gear in a cutting stroke which isinitiated with the ends of the tool teeth engaging the mid portion ofthe gear teeth, said cutting stroke comprising a relative translationeffective to move the contact on the gear teeth gradually to the endthereof toward said tool and a relative infeed radially of said gear,whereby cutting is effected by portions of said tool teeth substantiallyat an end thereof.

4. The method of crowning the teeth of a gear which comprises rotatingthe gear in mesh at crossed axes with a gearlike cutting tool, andeffecting a progressively deeper crowning cutting stroke which startswith the gear and tool positioned such that the common normal to theiraxes and as a result the limited contact between the teeth of the gearand tool is located substantially centrally-of the gear and at an edgeof said tool, said stroke being in a direction such that at its end thecommon normal to the axes is at the same edge of said tool and is at theedge of said gear such that said tool and gear be at opposite sides ofthe common normal.

5. The method of crowning gears which comprises running them in mesh atlimited crossed axes, employing only the end portions of the cutterteeth to effect cutting and effecting a progressively deeper crowningcut from the mid portions of the gear teeth toward those ends thereofwhich result in all except the said end portions of the meshing cutterteeth extending beyond the ends of meshing gear teeth at the end of thecutting stroke.

6. The method of crowning the teeth of a gear which comprises rotatingin mesh the gear and a gear-like cutting tool with the gear and tool atcrossed axes and the common normal to the axes and as a result thelimited contact between the teeth of the gear and tool at an edge of thetool, relatively translating the gear and tool longitudinally of thegear, and relatively moving the gear and tool toward each other whilethe gear and tool are being relatively translated from a position inwhich the common normal is located between the edges of the gear to aposition in which the common normal is located at an edge of the gearand the tool extends beyond the last mentioned edge.

MAX B. MENTLEY.

